1. Field of the Invention
The present invention relates to a wafer drying apparatus using a vapor of a combustible organic solvent such as isopropyl alcohol (IPA), and a fire-extinguishing method therefor.
2. Description of the Related Art
In the manufacturing process of a semiconductor device, a wafer drying apparatus is used to dry a semiconductor wafer by using a vapor of an organic solvent such as IPA after a cleaning step. The wafer drying apparatus using IPA includes an organic solvent bath made of quartz or the like and designed to store IPA. A heater for heating IPA to generate an IPA vapor is arranged at a lower portion in the bath. A cooler for cooling the IPA vapor and condensing it is arranged at an upper portion in the bath.
An elevator for holding a plurality of wafers and moving them vertically is arranged in the organic solvent bath. A wafer conveyed from a previous step (usually, a washing step) is placed on the elevator. The wafer is temporarily immersed in a vapor atmosphere at a lower portion in the bath, and moisture and the like adhering to the wafer are replaced with IPA. Thereafter, the wafer is moved to an upper portion in the bath to be dried.
A plurality of shutters are arranged around the organic solvent bath. While a drying process is not performed, the shutters are kept closed to isolate the bath from the outside so as to minimize the leakage of IPA.
As described above, the wafer drying apparatus includes the heater, and an organic solvent such as IPA is inflammable. Therefore, many of such drying apparatuses have fire-extinguishing mechanisms for quickly extinguishing a fire when IPA or the like is set on fire.
In a drying apparatus having such a fire-extinguishing mechanism, when a fire is detected by various types of sensors, an alarm is generated immediately, and the power to the apparatus is turned off. Subsequently, after an elapse of a predetermined period of time, e.g., 20 seconds, which is required for an operator to escape, CO.sub.2 gas is discharged from a nozzle arranged at an upper portion or the like in the bath. Note that the apparatus generally includes a manual switch to allow an operator or the like to start the fire-extinguishing mechanism upon a manual operation as well as detection of a fire by means of sensors.
As described above, in the IPA drying apparatus, when a fire is detected, or the manual switch is operated, CO.sub.2 gas for a fire-extinguishing operation is discharged after an elapse of about 20 seconds. With this operation, the safety of an operator and the like can be ensured, and an erroneous switching operation can be canceled. In this drying apparatus, however, a further improvement in safety is required.